Construction of Coordination Spaces with Narrow Pore Windows in Co-Based Metal–Organic Frameworks toward CO2/N2 Separation

Carbon emission reduction is an important measure to mitigate the greenhouse effect, which has become a hotspot in global climate change research. To contribute to this, here, we fabricated two Co-based metal-organic frameworks (Co-MOFs), namely, {[Co₃(NTB)₂(bib)]·(DMA)₂·(H₂O)₄}_n (DZU-211) and {[Co₃(NTB)₂(bmip)]·(DMA)₂}_n (DZU-212) (H₃NTB = 4,4',4″-nitrilotribenzoic acid, bib = 1,4-bis(imidazol-1-yl)-butane, bmip = 1,3-bis(2-methyl-1H-imidazol-1-yl)propane) to realize efficient CO₂/N₂ separation by dividing coordination spaces into suitable pores with narrow windows. DZU-211 reveals a 3D open porous framework, while DZU-212 exhibits a 3D double-fold interpenetrated structure. The two MOFs both possess large coordination spaces and small open pore sizes, via the bib ligand insertion and framework interpenetration, respectively. Comparatively, DZU-211 reveals superior selective CO₂ uptake properties due to its more suitable pore characteristics. Gas sorption experiments show that DZU-211 has a CO₂ uptake of 52.6 cm³ g^-1 with a high simulated CO₂/N₂ selectivity of 101.7 (298 K, 1 atm) and a moderate initial adsorption heat of 38.1 kJ mol^-1. Moreover, dynamic breakthrough experiments confirm the potential application of DZU-211 as a CO₂ separation material from postcombustion flue gases.